The present invention relates generally to the control of the storage environment for bulk-stored food grains, and, more particularly to controlling the storage environment in order to maintain the grain temperature and moisture in approximate equilibrium with the atmospheric temperature and moisture.
In the uncured state, i.e., before an equilibirum temperature/moisture condition is achieved, biochemical release of moisture from the seed to the surrounding atmosphere occurs, as does seed respiration which also releases moisture and heat. Recent advances in the grain conditioning art teach the use of constant airflows of specified volumes, according to seed moisture, to remove moisture as rapidly as it is released from the seed in order to effect a stable environment and achieve an equilibrium condition.
The removal of heat from the grain is as important as the removal of moisture, for any increase in grain temperature accelerates internal metabolism and respiration, thus causing a pyramiding accumulation of heat and moisture and an accompanying deterioration of grain. For example, if 1/2% of the dry weight of grain is consumed by respiration, the amount of heat produced by one bushel of grain is sufficient to raise the temperature of that bushel by approximately 67.degree. F. Multiply this by 10,000 bushels and even 100,000 bushels, since some storage structures hold that much, and it can readily be seen why removal of the heat from the grain is so critical.
The value of ventilation of grain in bringing it to a dry and cured condition is generally understood; but, the importance and the proper way of ventilating cured grain is not understood.
Generally, there are two approaches to controlling ventilation. The most common method is manual activation of fans when the operator decides ventilation is needed. This is unsatisfactory because of the possible error in human judgement. The other most common method is to install a thermostat with a sensor in the grain that responds to heating of the grain, thereby, activating the fan. This method is incorrect since it waits for a problem to develop, i.e., accumulation of heat and moisture, before activating ventilation.
Therefore, there is a need for a simple control for activating and deactivating ventilation equipment, whether the grain is in a cured or an uncured state, in response to the differential temperature condition that exists between the grain and the atmospheric air. As long as an equilibrium condition between the grain and its environment does not exist, the control equipment would preferably automatically respond by activating the ventilation equipment to bring about an equilibrium state (temperature/moisture) between the grain and the atmospheric air surrounding the bin.
Furthermore, as referred to above, grain respiration causes the accumulation of heat and moisture in the interstitial air around stored seeds on a continuing basis. Seed moisture content and seed temperature determine the rate of respiration and thus the rate of accumulation of heat and moisture in the interstitial air. Ventilation should provide constant removal of this heat and moisture. Wind-powered ventilation equipment can, by design, be adequate to provide for some constant removal of respiration heat and respiration-moisture; but, where large volumes of grain are involved or where prevailing winds are insufficient to induce adequate draft, electrically powered ventilation equipment is needed.
Further, for economic reasons it is desirable to prevent excess drying of grain, for the weight of moisture in grain determines bushels and thus income, as does weight of dry matter. Once grain moisture is brought to a 14-15% level, minimal ventilation is required to prevent heating through the summer months. Manual or thermostatic deactivation of a fan during these months is desirable to prevent unnecessary removal of moisture which will take place if automatic ventilation methods are employed.